Electrolytic apparatus for the recovery of rare refractory metals



Dec. 11, 1956 ATTORNEY United States Patent O I ELECTROLYTIC APPARATUSFOR RECOV- ERY OF RARE REFRACTORY METALS Norman C. Beese, Verona, andJohn W. Marden, East Orange, N. J., assignors to the United States ofAmerica as represented by the United States Atomic Energy CommissionApplication February 7, 1944, Serial No. 521,410

2 Claims. (Cl. 204-245) This invention relates to an apparatus forrecovering rare refractory metals and more particularly to improvementsin an apparatus for recovering rare refractory uranium in the form ofpowder is deposited on a cathode,

and then the refining of said powder. The present invention relates toimproved methods and apparatus for introducing rare refractory metalhalides, such as uranium halides known as green salts, into theelectrolysis bath for effecting the recovery of purer metal byelectrolysis.

Green salts, as they are prepared for example by the methods of saidcopending application contain small amounts of impurities such as boron,probably in the form of boron oxide, B203. The presence of boron as animpurity in electrolytic uranium is particularly undesirable even insmall quantities as it alters the properties of the uranium metal andincreases the difliculties inherent in using uranium.

The present invention provides a method of substantially eliminatingboron and similar impurities from the electrolysis bath, and hence amethod which avoids their inclusion in an electrolytically depositedrare refractory metal powder. Briefly, the stated difliculties may beovercome by introducing the salts into the fused salt electrolyte atpoints of substantially no electrical field and remote from the cathodeon which the rare refractory metal is to be deposited. By inserting asuitable anode shield in the electrolyte, points substantially free ofelectrical fields are provided where the rare refractory metal salt canbe heated and impurities therein converted to volatile substances andsubstantially all of these substances vaporized from the bath beforehaving an opportunity to come in contact with the metal deposited on thecathode.

It is the object of this invention to provide a method of recoveringelectrolytic rare refractory metals relatively free of impurities suchas boron.

It is another object of the invention to provide a method of addinggreen salt to fused salt electrolytes wherein certain impurities such asboron oxide will be converted to and liberated as vaporized compounds or2,773,826 Patented Dec. 1 1, 1956 It is a further object of theinvention to provide an improved apparatus for adding rare refractorymetal salts to a fused electrolyte at points remote from the vicinity ofa cathode in said electrolyte.

It is another object of this invention to provide apparatus to preventsalts added to a fused electrolyte from entering the electric field insaid electrolyte immediately upon contact with the electrolyte.

Other objects and advantages of the invention will be readily apparentto those skilled in the art upon reference to the following descriptionof a preferred method of electrolysis, and to the accompanying drawingsshowing preferred apparatus embodying our invention.

Fig. 1 of the drawings is an elevation view partly in section of theupper portion of an electrolysis cell and apparatus for feeding greensalt thereto. Fig. 2 is a plan sectional view of part of the apparatusof Fig. 1, taken on line 2-2 of Fig. 1.

An electrolysis cell' is indicated by the numeral 10. The cell 10, ofwhich only the upper portion is shown,

may be a carbon crucible about nine inches inside diam-- eter andtwenty-one inches deep, and is connected as an anode in the electrolysiscircuit. A number of such cells may be connected in parallel for thequantity production of rare refractory metals, such as uranium, as willbe well understood by those skilled in the art. An electrode 11, whichserves as a cathode, is positioned at approximately the center of thecell 10 and may be of any suitable shape and material, and supported byconventional means not shown. The cell 10 contains a fused salt bath 12,such as a mixture of calcium chloride and a sodium chloride,substantially filling the cell but having its surface 13 somewhat belowthe top of the cell. A graphite ring or shield 14 is supported in theupper portion of the cell 10 by means of a plurality of brackets 15extending between the ring 14 and the upper edge of cell 10. Thebrackets 15 should be of conducting material and serve to maintain thering or shield 14 spaced from and at the same potential as the cell 10.

The green salt feeding device includes a housing 16 connected to aconventional form of positive feeding apparatus, and a plurality offeeding tubes 17 extending from the housing 16 into the annular spacebetween the top of the cell 10 and the graphite ring 14, as shown inFig. l. The outlet ends 18 of tubes 17 may be above the electrolytesurface 13 as shown, or may extend slightly below the surface. The greensalt feeding device may be similar to that shown in the copendingapplication, Serial Number 521,409, filed February 7, 1944, by

Norman C. Beese, one of the joint inventors of the pres' ent invention,said application having been abandoned.

The method and operation of our present invention resides incontinuously feeding rare refractory metal salts into a fused saltelectrolyte at points remote from the cathode, and at points at whichthe electrical field in the fused electrolyte is negligible. For therecovery of uranium, the green salt may be continuously fed into housing16 by a conveyor of the type illustrated in said copending applicationof Beese. The green salt in housing 16 is conducted through tubes 17 tooutlet ends 18 between the shield 14 and the upper edge of the cell 10.The shield 14 is maintained at substantially the same potential as thecell 10 by means of the supporting brackets 15 of conducting material.The green salt material therefore enters the fused salt electrolyte 12at points between the shield 14 and the cell 10 at which points theelectrical field of the fused electrolyte is negligible. This factpermits the green salt to be heated to the temperature of theelectrolyte 12 quickly and causes at least some of the vaporizableimpurities therein to be liberated before a migration of ions due to theapplied voltage causes the impurities to reach cathode 1.1 for depositthereon. It is believed that undesirable impurities, such as boronoxide, B203, are converted to halides, such as boron halides, whichvaporize at temperatures below .the temperature of the fused: saltelectrolyte which is maintained at about 950- C.,.and are liberated fromthe electrolyte. As the impurities ingreenasalt intro duced at theperiphery of .the .electrolytehavearelatively long distance .to migrateto reach the centrally positioned cathode 11, the percentage ofvaporizable impurities remaining .unvaporized and available for depositon the cathode is relatively small. The introduction of greensaltcontinuously likewise improves .the quality of the electrodeposit ofuranium oncathodell, since there are no sudden additions of largequantities of green salt to the electrolyte andconsequently thecomposition .of the fused bath can be maintained @nearly. constant andthe impurities haveample time for conversion to vaporized products andliberation as vapors or gases.

The uranium electrodeposited on electrodes in accordance with ourimproved methods and apparatus is of increased purity in that the .boroncontent drops from several parts per .million to' little or no boroncontent in the deposited metal. Some of the elimination of the boronimpurity apparently takes .place in a space free of electrical fieldsbefore electrolysis begins. By retarding the electrolysis untilaftervsorne of the boron compounds have been converted to vaporizableproducts and liberated from the electrolyte as vapors or gases, rarerefractory metal of high purity and very low in boron content is morereadily obtained.

It will be readilyv apparent that numerous modifications and variationsmay be .made .in the abovedescribed methods and apparatus within thescope and spirit of our invention, as defined in the following claims.

-We claim:

1.v In apparatus for recovering a rare refractory metal by electrolysis,the combination comprising a crucible for containing a fusedelectrolyte, said crucible forming the anode of an electrolysis cell, acathode electrode supported from above and extending into said crucible.4 said electrode, said shield being electrically connected to saidcrucible to provide a space of substantially no electrical field betweensaid shield and said crucible wall.

2. In apparatus for recovering uranium metal by electrodeposition from afused electrolyte, the combination comprising a crucible for containingsaid electrolyte, said crucible having-a circular cross section andformingzthe anode;of anelectrolysis cell, a:cathode electrode supportedfrom above and extending into said crucible at the center thereof, anannular conducting-shieldextending into said crucible and surroundingsaid electrode,

means extending radially of the crucible between said shield and a wallof said crucible for spacingthe "shield from and electrically connectingthe shield to.saidtcrucible,

and means for feeding a metal salt to the electrolyte in said crucibleat points between the said shield and said crucible.

References ',Cited,in the file of this patent UNITED STATES PATENTS618,575 'Lyte Jan. 31, 1899 816,928 Lyons et al. Apr. 3, 1906 1,197,137McNitt Sept. 5, 1916 1,408,142 Seward Feb. 28, 1922 1,501,756 Downs July15, 1924 1,585,716 Hulin May 25, 1926 7 1,826,806 Mardenet al Oct. 13,1931 1,861,625 Driggs et al June 7, 1932. 1,913,145 Wait June 6, 19332,071,087 Philipp 2 Feb. 16,1937 2,401,821 Gardiner Junell, 19462,406,935 Wood et al. Sept. 3, 1946 FOREIGN PATENTS 74,959 Germany May17, 1894 730,197 France May 9,' 1932 386,790

OTHER REFERENCES Trornbe: Article in Transactions of the ElectrochemicalSoc, vol. 66, p. 58 (1934).

Great Britain Jan. 26, 1933

1. IN AN APPARATUS FOR RECOVERING A RARE REFRACTORY METAL BYELECTROLYSIS, THE COMBINATION COMPRISING A CRUCIBLE FOR CONTAINING AFUSED ELECTROLYTE, SAID CRUCIBLE FORMING THE ANODE OF AN ELECTROLYSISCELL, A CATHODE ELECTRODE SUPPORTED FROM ABOUT AND EXTENDING INTO SAIDCRUCIBLE CENTRALLY THEREOF, AND AN ELECTRICALLY CONDUCTING SHIELDPOSITIONED BETWEEN THE INNER WALL OF SAID CRUCIBLE AND SAID ELECTRODE,SAID SHIELD BEING ELECTRICALLY CONNECTED TO SAID CRUCIBLE TO PROVIDE ASPACE OF SUBSTANTIALLY NO ELECTRICAL FIELD BETWEEN SAID SHEILD AND SAIDCRUCIBLE WALL.